docs: clarify hook blocking exit code

[MiladZarour]

Summary

• Clarify that only exit code 2 blocks Claude Code hook execution
• Note that exit code 1 and other non-zero codes are non-blocking
• Update the Bash hook example comments and hook-development troubleshooting docs

Motivation

Fixes #44707.

The current docs mention that “Other” exit codes are non-blocking, but this is easy to miss because developers often expect exit(1) / sys.exit(1) to block failed enforcement hooks.

Testing

• Ran git diff --check
• Ran python -m py_compile examples/hooks/bash_command_validator_example.py